Lenovo y50k dual boot win 10 and win 8.1 issue?

I have lenovo y50 4k laptop with 1tb hdd, 16gb ram and 4gb nvidia 860 gtx.
I attempted to do a dual boot with win 8.1 and win 10. Initially it worked well and fine up to 2 months. Suddenly it started a slow boot for win 8.1 and kept on. I googled almost everything but couldn t find any solution.
Any help would be appreciated.

Contact Micro$oft for the customer support that you have already paid for.

Do you never read the news Do you want to be paying for annual subscription fees and paying for other M$ cloud services that's is what going to happen in August. Every W10 users will have to sign up to pay Annual fees, for WaaS (windows as a Service) and extra payments for SaaS (Software as a Service)

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